JavaScript - Set Interval

The window object allows execution of code at specified timed intervals. These time intervals are called timing events.

The four key methods to use with JavaScript are:

• setTimeout(function, milliseconds) executes a function, after waiting a specified number of milliseconds
• clearTimeout() method clears a timer set with the setTimeout() method
• setInterval(function, milliseconds) same as setTimeout(), but repeats the execution of the function continuously
• clearInterval() clears a timer set with the setInterval() method

The window.setInterval method calls a function or evaluates an expression at specified intervals (in milliseconds). The setInterval() method will continue calling the function until clearInterval() is called, or the window is closed.

This example displays the current time (the setInterval() method will execute the function once every 1 second, just like a digital watch). Once you click the button, it will call the clearInterval and stop the code.

const ShowMessage = () =>
{
    document.getElementById("demo1").innerHTML = "Hello World!";
    clearInterval(intervalTimerId);
}

const UpdateDisplay = () =>
{
    document.getElementById("demo1").innerHTML = `Showing message in ${countdown}.`;
    countdown--;
}

const StopCountdown = () =>
{
    console.log("Stopping clock...");
    clearInterval(intervalTimerId);
    clearTimeout(timeoutTimerId);
};

let countdown = 10;
let delay = 10000;
let timeoutTimerId = setTimeout(ShowMessage, delay);
let intervalTimerId = setInterval(UpdateDisplay, 1000);

http://www.w3schools.com/jsref/met_win_setinterval.asp

https://www.w3schools.com/jsref/met_win_clearinterval.asp

http://www.w3schools.com/js/js_timing.asp